I've gone ahead and rated this four stars as it would have put Nintendo's Wii U in a better light had it been included as standard. I guess they were doing everything possible to keep the overall price of the console as low as possible.
However, now I've installed it, the battery has given my Wii U a new lease of life. So much so that I've taken to using the gamepad almost as a tablet replacement for browsing the Internet whilst watching T.V and playing Mario Kart 8 whilst being sat in other locations of my house. Beforehand using the gamepad was a hit and miss afair as you couldn't go that far from it's power lead umbilical cord. I've not tested the batteries full charge span yet but I've more confidence in it and I'm less concerned about it dying on me at a critical moment during game play.
Well worth buying, especially since Nintendo's strong E3 game lineup for the latter part of 2014/early 2015. Blow the dust off your Wii U!